Feat: Add setup command with check and error

The `setup` command creates a game instance for a channel.
It also has a check to see if one is already setup and a error handler to deal in that case.
I don't think that the check functions can be methods so the 'hack' is to use `ctx.cog` instead of `self` to get the cog instance.
There is also a function to check for the inverted condition preventing double defining every check.

src/cogs/basic_game.py

@@ -4,6 +4,17 @@
 from discord.ext import commands
 
 
+# checks
+
+
+def is_not(check):
+	return lambda ctx: not check(ctx)
+
+
+def is_setup(ctx):
+	return ctx.channel in ctx.cog.sessions
+
+
 class Cog(commands.Cog):
 	"""A base game cog that has a collection of basic game commands and checkers"""
 
@@ -14,6 +25,20 @@ class Cog(commands.Cog):
 		self.group = next(c for c in self.get_commands() if c.name == 'group')
 		self.group.name = self.qualified_name.lower()
 
+	@commands.group(invoke_without_command=True)
+	async def group(self, ctx):
+		await ctx.send("try info")
+
+	@group.command()
+	@commands.check(is_not(is_setup))
+	async def setup(self, ctx):
+		"""Creates a game instance for this channel"""
+		self.sessions[ctx.channel] = self.session_cls()
+
+	@setup.error
+	async def setup_handler(self, ctx, error):
+		await ctx.send(f"A game of is already setup in this channel")
+
 
 class Session:
 	"""A base class for holding channel specific information and setting up a game"""